This invention relates to a method for forming a pad character in a key top for a push button switch which is used for a data input unit for a mobile communication equipment, a switch unit or the like and a method for manufacturing a cover member for a push button switch, and more particularly to a method for irradiating a key top with a laser beam to form an indication such as a character or the like in the key top.
A push button switch for a data input unit for a mobile communication equipment such as a cellular phone, a key board for a personal computer or the like is generally constructed by mounting a cover member directly on a circuit board. In such a push button switch, a substrate which includes a plurality of movable sections is formed of a rubber elastomer. The movable sections are each provided on a front surface thereof with a key top and on a rear surface thereof with a movable contact. The key top is formed on a top surface thereof with a figure, a character or the like by printing, to thereby provide a cover member.
In the cover member thus constructed, the top surface of each of the key tops functions as an operation section or a pressed surface with which a finger of an operator is contacted, when the cover member is mounted on the circuit board to constitute the push button switch. Thus, use of the push button switch for a long period of time causes the figure, character or the like on the top surface of the key top to be worn due to contact with the finger, leading to a deterioration in visibility of the figure or the like.
A cover member intended to improve wear resistance of a character, a figure or the like on a top surface of a key top is proposed in Japanese Patent Application Laid-Open Publication No. 169360/1995. More specifically, the publication discloses a method for manufacturing a cover member wherein a key top is formed on a top surface thereof with a recess of 5 to 50 .mu.m in depth in any desired design by means of a forming die concurrently with formation of the key top, and then a colored section is formed of an ink of 150 to 400 p (poise) in the recess by screen printing by means of a polyester screen which was subjected to plasma processing so as to have a mesh density of 300 to 500 meshes/inch.
However, the method disclosed in the Japanese publication requires to form the forming die for the key top with fine projections for forming the recess, so that working or machining of the forming die is highly troublesome and durability of the forming die is deteriorated. Also, the method requires formation of the recess and applying of the coloring ink in the recess, to thereby increase the number of steps in the manufacturing, leading to an increase in manufacturing cost. Further, use of the cover member for a prolonged period of time often causes falling-off of the coloring agent or ink from the recess, so that the key top is deteriorated in being comfortable to fingers.